At Windhowl, search for an NPC called A Wounded Guard (located at the first house at the left as you enter the town).
Speak to him and he will tell you that a Troll wounded him.
He will also ask you to kill the Troll.
Go to Troll's Lair (west from caves) and find Mhorgwolth the troll. Kill him and return to Windhowl .
Say Troll to the Wounded Guard and he will reward you with a Shield of Windhowl.
Gain: